The present invention relates to a steering lock mechanism for restricting rotation of a steering wheel shaft.
A steering lock mechanism is often used in vehicles to prevent theft. In the prior art, a typical steering lock mechanism includes a lock bar and a socket, which is formed in the outer surface of a steering shaft that is rotated by a steering wheel. The lock bar is fitted into the socket to restrict rotation of the steering shaft.
More specifically, the steering shaft is retained in a cylindrical steering column. A lock body, which accommodates the lock bar, and a bracket are arranged on the steering column so as to sandwich the steering column. A flange extends from each end of the lock body and the bracket. The flanges of the lock body contact the flanges of the bracket. A threaded hole is formed in each flange of the lock body. A bolt hole is formed in each flange of the bracket in alignment with the threaded hole of the corresponding lock body flange. A bent portion, which is bent away from the lock body in the axial direction of the lock bar, is formed at an edge of each bracket flange to provide space for a bolt. A bolt is inserted through each bolt hole of the bracket and mated with the corresponding threaded hole of the lock body so as to fasten the bracket to the lock body (refer to, for example, Japanese Laid-Open Patent Publication No. 2005-162053).
In recent vehicles, there is a tendency of lowering the location of the instrument panel to improve visibility. This has reduced space for the steering lock mechanism. Thus, there is a demand for smaller steering lock mechanisms.
Accordingly, referring to FIG. 11, a hinged structure 71 has been employed in the prior art to fasten a bracket 53 to a lock body 67. More specifically, the hinged structure 71 includes a pin support 72 for supporting a pin 76. The bracket 53 includes a hook 73, which is hooked to the pin 76. A fastening portion 81, which includes a flange 83, is defined opposite to the hinged structure 71. A bolt 86 is inserted through the flange 83 to fasten the bracket 53 to the lock body 67. As viewed in FIG. 11, to provide space-for the bolt 86, the upper surface 83a of the flange 83 is located at level L1, which is higher than the upper surface 72a of the pin support 72 located at level L2. Accordingly, the hinged structure 71 provides extra space L, which corresponds to the difference between levels L1 and L2.
However, with the above steering lock mechanism of the prior art, when a lock bar 70 is inserted into a socket 63 to lock and restrict rotation of a steering shaft 59 as shown in the state of FIG. 11, forcible rotation of the steering wheel (not shown) would apply a strong torque to the steering shaft 59. This may flex and displace the steering shaft 59 in the direction shown by arrow X.
In such a case, stress would also be applied to the bracket 53 in the direction shown by arrow X. As a result, stress would be applied to the hook 73 of the bracket 53 in the direction of arrow Y as shown in FIG. 12A. This may deform the bracket 53 as shown in FIG. 12B. In this state, the application of further torque by the steering wheel would detach the bracket 53 from the lock body 67 and release the lock bar 70 from the steering shaft 59. Such strong torque may be applied to forcibly enable rotation of the steering shaft in an attempt to steal the vehicle.